Hot Motor

[IBechir]

I encountered an end-suction installation, 2+1 pumps in parrallel, pumping clean water from a ~27'C makeup source. It is a closed hydraulic system and the pumps have a VFD. The pump in question was running at 50Hz for an hour and the motor enclosure was too hot to hold. I'de say 40-50'C.

I checked and found that the selection was 40-50% efficiency from the pump curve (I know its a terrible selection).

I don't know what to make of the motor enclosure temperature, is it because of the poor effieciency, what is considered a normal temperature rise?

I haven't checked the current yet but the contractor ensures that it is below max. rated. Pumps are rotated and the issue is common to all pumps. The volute sounds quiet; no signs of air entrainment/cavitation and most of the noise is from the motor (78dB standing right next to it). Pumps = 36lps@3.5bar each.

Much obliged to all feedback.

 

[Pumpsonly]

You did not mention about ambient temp . 40-50 C motor surface temp.is very -very normal.

As standard , motor are designed for 40C ambient temp. With allowable Class B temp rise of 80C means the inner winding temp can go upto 120C.
With VFD you need to check the motor is not run below a certain RPM. depending on the loading. But with centrifugal pump
it is not so much a concern as for PD pumps.

Just search the web for VFD motor application and you will find more info than you can handle.

 

[IBechir]

Max ambient over the past week was 37'C because the air conditioning is not working yet.

 

[electricpete]

50C skin temperature in 37C ambient even at low load does not suggest any problem whatsoever to me.

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(2B)+(2B)' ?

 

[LittleInch]

"Too hot to hold" is not exactly a definitive temperature check - Get some proper readings then come back to the post. Normally a human can just stand fleeting contact with 60-70C without getting burnt/pain - touch and lift off instantly, but it is a variable thing depending, literally, on the thickness of your skin and pain threshold. If you're really concerned, get an IR thermometer.

Also check your motor spec - many include temperature probes inside the windings which can be checked or used to trip the motor above the maximum defied by the vendor.

However I agree with the posters above - I don't think you've got a serious issue here, but I suggest you get more information.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way